The above Military Specifications for the CARC, provide the requirements imposed in order to comply with the allowable range of values of optical and radiometric properties. Thus, it provides the allowable range of values of optical and radiometric properties. For example, it quotes the X,Y tristimulus colour coordinates, the infra-red diffuse reflectance at 1.5 micrometer, and the specular reflectance. The paint compositions according to the above Military Specification, include two main components:
Part A, which consists of phthalic trimethylol propane ester combined with a primer, extender, pigments and volatile solvents, and PA1 Part B, consisting of an aliphatic isocyanate prepolymer combined with volatile solvents. PA1 a special family of pigments, which are transparent to thermal infra-red radiation selected from a metal oxide calcined at a temperature of above 600.degree. C. and a paste of a metal flakes; PA1 a binder selected from alkyds, polyurethanes, vinylic and epoxy compounds, silicones, acrylic resins and mixtures thereof; PA1 an extender selected from polyolefins and substituted polyolefins, and PA1 the other common constituents normally present in a paint composition. PA1 (a) a highly reflective metallic substrate; PA1 (b) a layer of semiconductor pigment which possesses the property to absorb in the visible range, transparent to infra-red radiation and a low enough refractive index, and PA1 (c) a binding overcoat of alkali metal silicates cured at a temperature in the range of 150.degree. C. to 550.degree. C. PA1 an extender selected from polyolefins and substituted polyolefins; PA1 a pigment selected from a metal oxide calcined at a temperature of above 600.degree. C. and a paste of metal flakes or any mixture thereof; PA1 a binder, and PA1 a solvent system to dissolve the components in the paint compositions, PA1 high reflectivity in the thermal infra-red, generally encountered in the range of between 0.1 to 0.7; PA1 low gloss; PA1 a controllable colour, and PA1 Chemical Agent Resistant Coating properties.
However,the above Military Specification does not mention anything in respect to the reflectivity in the thermal infra-red region. Furthermore, once special reflecting additives and auxiliaries are mixed in the paint system, said Specification does not impose any requirement in respect to the compatibilty with the paint system or the durability of the coating with the respective paint composition. Therefore, it is required to carry out a proper selection that the respective pigments should be compatible with the paint system, without affecting the stability of the paint or the durability of the coating. In our above U.S. patent application Ser. No. 08/344,567 there were disclosed paint compositions possessing a low gloss and high reflectance in the infra-red range of between 3 to 14 micrometers. These compositions include:
According to U.S. Pat. No. 4,034,129, a coating system is described which possesses a high absorptivity in the visible range and low infra-red emissivity. The system comprises:
According to the U.S. Pat. No. 4,310,596, a coating for solar collector is claimed, comprising a finely divided black spinel pigment based on a cobalt or copper oxide. The selective properties of this coating such as-infra-red emittance below 0.35, are obtained only at a very thin thickness of about 1 .mu.m, while a thickness of 4 .mu.m and above, gave rise to infra-red emittance in the range of 0.49 to 0.62, which are not useful in the present invention.
In the U.S. Pat. No. 4,311,623, a low infra-red emitting paint is described comprising a non-leafing aluminum powder, aluminum oxide, antimony trisulfide and a silicone alkyd resin. It is mentioned that a drop occurs in the emmissivity in the 3-5 .mu.m range from 0.797 to 0.463.
It is an object of the present invention to provide paint compositions possessing high infra-red reflectivity and low gloss, imparting at the same time coating conforming the Military Specification requirements of the CARC type. It is another object of the present invention, to provide paint compositions which impart the coating conforming the Military Specification requirements of the CARC type, without affecting the improved optical properties of said paint compositions.